Although not restricted to it, the invention in particular relates to the check of bank notes, checks or coupons which are provided with machine-readable security features that can be optically checked in the invisible spectral region, in order to e.g. check or determine the authenticity and/or the nominal value of the document of value. Such security features detectable in the invisible spectral region, for example, can be substances emitting or absorbing in the ultraviolet or infrared (for short: IR) which are contained in the printing ink or in the bank note paper.
Systems for optically checking such documents of value are known, for example, from DE 10007887 A1, DE 19701513 C2, WO 2004/036508, U.S. Pat. No. 5,757,001 or EP 1233261 A1.